Spinal implant

ABSTRACT

A spinal implant is inserted between adjacent vertebrae to function as an disk prosthesis. The prosthesis has two plates fastened to adjacent vertebrae facing each other. The facing sides of the plates each have a depending skirt formed as concentric arcs of about 90 degrees. The skirts are either bowed or tapered in the axial direction. A protrusion is centrally located between the arcs on one plate and a depression is centrally located between the arcs of the other plate. A spring mechanism is centrally located on one of the plates to provide axial compression. The plates are oriented to each other with the concentric arcs of each interrupted skirt at 90 degrees and the protrusion is engaged in the depression. The plates are then rotated about 90 degrees and the opposed arcs of one plate interlock with the opposed arcs of the other plate to prevent separation in the axial direction.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.10/792,339, filed Mar. 2, 2004.

FIELD OF THE INVENTION

This invention relates to orthopedic surgery and, in particular, spinalimplants for replacement of ruptured or excised spinal disks.

BACKGROUND OF THE INVENTION

Several attempts have been made to design a spinal prosthesis forreplacement of missing or excised disk material that replicates thefunctions of the missing tissue. U.S. Pat. No. 4,759,769 to Hedman et aldiscloses a artificial disk device in which two plates are attached tothe adjacent vertebrae by bone screws inserted through flanges on theplates. A spring biasing mechanism is captured between the plates tosimulate the actions of the natural disk material. U.S. Pat. No.5,246,458 to Graham and U.S. Pat. No. 6,228,118 to Gordon disclose otherintervertebral implants with arcuate flanges used to connect the deviceto adjacent vertebra. Graham also teaches a resilient structure.

The patents to Marnay, U.S. Pat. No. 5,314,477, Buttner-Janz et al, U.S.Pat. No. 5,401,269, Yuan et al, U.S. Pat. No. 5,676,701, and Shelokov,U.S. Pat. No. 6,039,763, all are directed to the design of the opposingfaces of the adjacent plates of an implant to provide a limiteduniversal joint to simulate the natural movement of the spine.

U.S. Pat. No. 5,683,465 to Shinn et al teaches two plates with bowshaped skirts which are interlocked.

SUMMARY OF THE PRESENT INVENTION

A spinal implant for insertion between adjacent vertebrae to function asan disk prosthesis. The prosthesis is formed from two plates fastened toadjacent vertebrae facing each other. The facing sides of the plateseach have a depending skirt formed as concentric arcs of about 90degrees. The skirts are either bowed or tapered in the axial direction.A protrusion is centrally located between the arcs on one plate and adepression is centrally located between the arcs of the other plate. Aspring mechanism is centrally located on one of the plates to provideaxial compression. The plates are oriented to each other with theconcentric arcs of each interrupted skirt at 90 degrees and theprotrusion is engaged in the depression. The plates are then rotatedabout 90 degrees and the opposed arcs of one plate interlock with theopposed arcs of the other plate to prevent separation in the axialdirection.

Therefore, it is an objective of this invention to provide a spinalimplant for axial support of the spinal column which replicates thedimensions and function of an intervertebral disk.

It is another objective of this invention to provide a kit including allthe components for assembly and surgical placement of an artificialspinal disk.

It is a further objective of this invention to provide a method ofassembly of the components of the kit which results in an axiallyinterlocked spinal implant.

It is yet another objective of this invention to provide a modified balland socket joint between two plates attached to adjacent vertebraepermitting axial rotation, lateral bending, vertical tilting and axialcompression.

It is a still further objective of this invention to provide shapedinterrupted skirts on two plates which act as stop limits for tiltingand bending.

It is another objective of this invention to provide an axiallyresilient ball and socket joint.

Other objectives and advantages of this invention will become apparentfrom the following description taken in conjunction with theaccompanying drawings wherein are set forth, by way of illustration andexample, certain embodiments of this invention. The drawings constitutea part of this specification and include exemplary embodiments of thepresent invention and illustrate various objects and features thereof.

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective of the disassembled kit of this invention;

FIG. 2 is a perspective of the assembled spinal implant of thisinvention with alternative fasteners;

FIG. 3 is a frontal view, partially in section, of the assembled implantof this invention showing axial rotation;

FIG. 4 is a frontal view, partially in section, of a modification of theassembled implant.

FIG. 5 is a frontal view, partially in section, of the assembled implantshowing a positive bend;

FIG. 6 is a side view, partially in section, of the assembled implantshowing flexion/extension;

FIG. 7 is a perspective of the assembly position of the kit of thisinvention;

FIG. 8 is a side view, partially in section, of the implant showing thealternative location of the spring assembly; and

FIG. 9 is a side view, partially in section, of the implant showing analternative location of the spring assembly.

DETAILED DESCRIPTION OF THE INVENTION

The spinal implant 10, shown in FIG. 1, has three major components, anupper plate 11, a lower plate 12 and a leaf spring mechanism 50. Forpurposes of illustration only, the upper plate 11 is shown with a domeshaped depression 13. Of course, the position of the plates can bereversed, in use. Both upper plate 11 and lower plate 12 have a planform substantially the size and shape of the end wall of the vertebrabetween which the implant will be placed to produce the maximum area ofcontact between the implant and the vertebra for stability and support.Obviously, different sized plates are necessary because of thedifference in size of vertebra within a spinal column and the differentsizes or ages of patients.

The upper plate 11 has a planar surface 14 for contact with the end wallof a vertebra and an opposite disk surface 15. Depending from the disksurface is an interrupted skirt 16 with opposed arcs 17 and 18. The arcsare approximately 180 degrees apart at their centers and extend about 90degrees. The diameter of the arcs is less than the periphery of theplate 11 leaving a horizontal flange 19. Centrally located within thesemi-circular arcs is the dome shaped depression or concavity 13.

The lower plate 12 has a planar surface 20 for contact with the end wallof a vertebra and an opposite disk surface 21. Upstanding from the disksurface is an interrupted skirt 22 with opposed arcs 23 and 24. The arcsare approximately 180 degrees apart at their centers and extend about 90degrees. The diameter of the arcs is less than the periphery of theplate 12 leaving a horizontal flange 25. Centrally located within thesemi-circular arcs is the protrusion 26. The end 27 of the protrusion isrounded and shaped to closely fit the contours of the depression 13. Theprotrusion 26 is of such dimensions as to support the weight of thespinal column.

As shown, though the relationship could be reversed, the opposed arcs 17and 18 of the depending interrupted skirt 16 are concentric with theopposed arcs 23 and 24 of the upstanding interrupted skirt and of lesserdiameter allowing rotation of the plates relative to each other withsurface contact between the outer surface 28 of the depending arcs andthe inner surface 29 of the upstanding arcs.

As shown in FIG. 1, each of plates of the spinal implant has an fastenerflanges 30 and 31 approximately normal to the vertebra contactingsurfaces 14 and 20. The flanges have apertures 32, 33 which cooperatewith bone screws to mount the spinal implant on the vertebra. Thefastener flanges 30, 31 may be on the anterior surface or posterior ofthe vertebra. Also, in FIG. 2, an alternative fastener is shown in theform of spikes 34 which are driven into the end walls of the adjacentvertebra. Of course, the two fasteners may be used together.

The spinal implant provides support and range of motion similar to thenatural joint in that the plates 11 and 12 may rotate axially, as shownin FIG. 3, limited by natural anatomical structures. To simulate thecompression of the natural disk during normal activities, such aswalking, a spring mechanism 50 is placed in the vertical axis of theplates 11 and 12. The protrusion 26 is telescopically housed in a cavity51. The protrusion is supported on a leaf spring 52. As shown in FIG. 3,the spring 52 has two spherical leafs 53 and 54 in opposition to eachother. The spring is held in the cavity 51 by the disk side plate 55. Byabsorbing some of the longitudinal loads, the prosthesis lessens thestresses on the adjacent natural disks.

The spine may bend laterally, as shown in FIG. 4, and tilt medially inflexion/extension, as shown in FIG. 5, in a range of approximately + or−10 degrees from center. The implant also provides limitation of thesemovements through interaction of the depending arcs and the upstandingarcs.

As shown in FIG. 6, the components of the kit are connected together byorienting the interrupted skirts 16 and 22 at 90 degrees to each otherthen placing the rounded end 27 of the protrusion 26 in the concavity13. This action overlaps the interrupted skirts vertically. The platesare rotated through 90 degrees relative to each other, as shown in FIG.7. This rotation aligns the depending opposed arcs with the upstandingopposed arcs and interlocks the plates in a movable joint that cannot beseparated axially. The outer surface 28 of the interrupted skirt 16slidably contacts the inner surface 29 of the interrupted skirt 22. Thecontacting surfaces are spherical or bowed, as shown in FIGS. 3 and 4,forming another ball and socket joint with the bottom edge of thedepending arc 23 of a larger diameter than the top edge of theupstanding arc 17 by which the plates are interlocked. Of course, theinner and outer surfaces may be straight or tapered and spaced apart toallow for bending and tilting. The components are made from materialsthat are suitable for implantation in the living body and have therequisite strength to perform the described functions withoutdeformation, e.g., surgical stainless steel, titanium, and alloys ofeach, coated metals, ceramics, ceramic coatings, and polymer coatings.The surfaces may be coated or otherwise treated to promote bonein-growth. In the high wear areas, such as the rounded end of theprotrusion and the depression, coatings or inserts may be used toprevent galling and permit repair.

FIG. 8 illustrates a modification of the spring location. In thisembodiment, the contacting surfaces 28′ and 29′ of the interruptedskirts are held in tension by the spring mechanism 50 mounted betweenthe depression 13 and the disk side of the plate. The depression 13 isformed on a slidable plug 56 in a bore 57 of the plate. The leaf spring53, 54 is captured between the plug 56 and the disk surface of theplate. The spherical leaf spring, as shown, has two leafs with each leafhaving a central aperture 60. As the spine is subjected to dynamicforces originating with physical activity, the spring mechanism 50 willdampen the shocks and the artificial disk will lessen the transmittal ofthese shocks to vertebrae on either side of the prosthesis.

In FIG. 9, the protrusion 26 is shown with the spherical leaf spring 53,54 fixed to the rounded end 27. The central aperture 60 of spring leaf54 is attached to the protrusion about its periphery 61. The centralaperture of the leaf 53 is aligned with the protrusion. The depression13 is modified with a larger entrance 58 of sufficient diameter toaccept the spherical leaf spring. The shoulder 59 provides the reactionsurface for the spring.

The kit contains plates with protrusions and skirts of varying lengthsto allow selection of components for an implant with the axial dimensionsubstantially the same as the thickness of the disk the implant willreplace. The kit may also contain upper and lower plate components ofvarying sizes.

A number of embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiment but only by the scope ofthe appended claims.

1. A spinal prosthesis kit for placement between adjacent vertebrae toreplace disk material comprising a first plate and a second plateadapted to interlock about a central axis, a spring in said central axisadapted to resiliently flex perpendicularly to said central axis, saidfirst plate having a planar vertebrae engaging side and a disk side, afirst interrupted skirt on said disk side extending approximately normalto said first plate, said skirt formed as opposing arcs, a depression insaid central axis of said disk side of said first plate centrallylocated between said opposing arcs, said second plate having a secondplanar vertebrae engaging side and a second disk side, a secondinterrupted skirt on said second disk side extending approximatelynormal to said second plate, said second skirt formed as opposing arcs,a protrusion on said central axis of said second disk side of saidsecond plate centrally located between said opposing arcs whereby saidfirst plate is adapted to contact a vertebrae and said second plate isadapted to contact an adjacent vertebrae with said depression forming abearing surface for said protrusion along said central axis that doesnot interlock therewith, whereby said first and second interruptedskirts interlock to prevent axial separation of said first and secondplates forming a universal joint.
 2. A spinal prosthesis kit forplacement between adjacent vertebrae of claim 1 wherein said firstinterrupted skirt and said second interrupted skirt are concentric in aplane parallel with said first and second plates, said opposed arcs ofsaid first interrupted skirt are adapted to contact said opposed arcs ofsaid second interrupted skirt.
 3. A spinal prosthesis kit for placementbetween adjacent vertebrae of claim 2 wherein said opposed arcs of saidfirst interrupted skirt and said second interrupted skirt extendapproximately 90 degrees relative to each of said first interruptedskirt and said second interrupted skirt, respectively.
 4. A spinalprosthesis kit for placement between adjacent vertebrae of claim 2wherein said opposed arcs of said first interrupted skirt and saidopposed arcs of said second interrupted skirt are concentric segments ofa circle in a plane parallel to said first and second plates wherebysaid concentric segments of said first interrupted skirt are adapted tocontact said concentric segments of said second interrupted skirt toform an interlocked universal joint.
 5. A spinal prosthesis kit forplacement between adjacent vertebrae of claim 1 wherein said opposedarcs of said first interrupted skirt and said opposed arcs of saidsecond interrupted skirt are concentric segments of a circle in a planeparallel to said first and second plates whereby said concentricsegments of said first interrupted skirt are adapted to contact saidconcentric segments of said second interrupted skirt to form aninterlocked universal joint.
 6. A spinal prosthesis kit for placementbetween adjacent vertebrae of claim 5 wherein said first plate and saidsecond plate each includes a fastener on said disk side adapted to fixsaid plate to the respective vertebrae.
 7. A spinal prosthesis kit forplacement between adjacent vertebrae of claim 6 wherein a first fasteneron said first plate and a second fastener on said second plate eachincludes a first flange and a second flange extending approximatelynormal to said first vertebrae engaging side and said second vertebraeengaging side, respectively, at least one aperture through said firstflange and said second flange for accepting a bone screw whereby saidfirst plate and said second plate may be attached to adjacent vertebrae.8. A spinal prosthesis kit for placement between adjacent vertebrae ofclaim 1 wherein said first plate includes a first fastener and saidsecond plate includes a second fastener each said fastener having afirst flange and a second flange extending approximately normal to saidfirst vertebrae engaging side and said second vertebrae engaging side,respectively, at least one aperture through said first flange and saidsecond flange for accepting a bone screw whereby said first plate andsaid second plate may be attached to adjacent vertebrae.
 9. A spinalprosthesis kit for placement between adjacent vertebrae of claim 1wherein said first interrupted skirt and said second interrupted skirtare tapered.
 10. A spinal prosthesis kit for placement between adjacentvertebrae of claim 1 wherein said first plate includes a cavity betweensaid depression and said vertebrae side, a leaf spring secured in saidcavity, said protrusion adapted to flex said leaf spring resulting inresilient compression.
 11. A spinal prosthesis kit for placement betweenadjacent vertebrae of claim 1 wherein said second plate includes acavity between said protrusion and said vertebrae side, a leaf springsecured in said cavity, said protrusion adapted to flex said leaf springresulting in resilient compression.
 12. A spinal prosthesis forplacement between adjacent vertebrae for resilient axial supportcomprising a first plate and a second plate, said first plate having aplanar vertebrae engaging side and a disk side, a first fastener on saidplanar side for engaging a vertebrae, a first interrupted skirt on saiddisk side extending approximately normal to said first plate, said firstinterrupted skirt formed as opposing arcs, a depression in said diskside of said first plate centrally located between said opposing arcs,said second plate having a second planar vertebrae engaging side and asecond disk side, a second fastener on said second planar side forengaging a vertebrae, a second interrupted skirt on said second diskside extending approximately normal to said second plate, said secondskirt formed as opposing arcs, a protrusion on said second disk side ofsaid second plate centrally located between said opposing arcs, saidprotrusion inserted in said depression, said depression forming abearing surface for said protrusion that does not interlock therewith, aspring means for resilient compression between said depression and saidprotrusion, said first interrupted skirt and said second interruptedskirt being concentric in a plane parallel with said first and secondplates, said opposed arcs of said first interrupted skirt contactingsaid opposed arcs of said second interrupted skirt, said opposed arcs ofsaid first interrupted skirt and said opposed arcs of said secondinterrupted skirt being concentric segments of a circle in a planeparallel to said first and second plates whereby said concentricsegments of said first interrupted skirt contact said concentricsegments of said second interrupted skirt to form an interlockeduniversal joint.
 13. A spinal prosthesis for placement between adjacentvertebrae of claim 12 wherein said concentric segments are adapted torotate approximately plus or minus 10 degrees relative to each other.14. A spinal prosthesis kit for placement between adjacent vertebrae ofclaim 12 wherein said first plate includes a bore centrally locatedbetween said opposed arcs, a spring spanning said bore, said disk sideof said bore forming said depression, said protrusion adapted to flexsaid spring resulting in resilient compression.
 15. A spinal prosthesiskit for placement between adjacent vertebrae of claim 12 wherein saidsecond plate includes a cavity in said disk side, said protrusionslidably telescoped in said cavity, a leaf spring secured in saidcavity, said protrusion adapted to flex said leaf spring resulting inresilient compression.
 16. A method of assembly of a resilientlycompressible spinal prosthesis comprising the steps of: a) providing afirst plate, said first plate having a planar vertebrae engaging sideand a disk side, a first interrupted skirt on said disk side extendingapproximately normal to said first plate, said skirt formed as opposingarcs, a depression forming a bearing surface in said disk side of saidfirst plate centrally located between said opposing arcs; b) providing asecond plate having a second planar vertebrae engaging side and a seconddisk side, a second interrupted skirt on said second disk side extendingapproximately normal to said second plate, said second skirt formed asopposing arcs, a protrusion on said second disk side of said secondplate centrally located between said opposing arcs; c) providing aspring between said first plate and said second plate; d) orienting saidfirst plate and said second plate parallel with each other with saidinterrupted skirt of said first plate located between said opposing arcsof said second plate; e) moving said interrupted skirt of said firstplate between said opposing arcs of said second plate and engaging saidprotrusion in said bearing surface of said depression that does notinterlock therewith; and f) rotating said first plate and said secondplate about an axis relative to each other until said interrupted skirtof said first plate contacts said opposing arcs of said second plate;and g) compressing said spring with said protrusion whereby saidinterrupted skirt of said first plate and said interrupted skirt of saidsecond plate are interlocked to prevent axial separation.
 17. A methodof assembly of a spinal prosthesis of claim 16 comprising the steps of:a) pivoting said protrusion in said depression plus and minusapproximately 10 degrees from the axis in the direction of said opposedarcs and b) said pivoting limited by said interrupted skirt of saidfirst plate contacting said second plate.
 18. A method of assembly of aspinal prosthesis of claim 14 comprising the steps of: a) pivoting saidprotrusion in said depression plus and minus approximately 10 degreesfrom the axis in the direction away from said opposed arcs, and b) saidpivoting limited by said interrupted skirt of said first platecontacting said interrupted skirt of said second plate.